Despite careful efforts at sanitation in packing house operations, there will be present on the surface of carcasses of freshly slaughtered hogs substantial quantities of bacteria. It is particularly important that such bacteria not be allowed to multiply while the carcass is still warm; and to the extent feasible, such bacteria should be destroyed.
One process presently in use is described in U.S. Pat. No. 3,745,026 entitled "Carcass Chilling Process". In this process, chlorine and/or hypochlorites are mixed with water to form hypochlorous acid which is sprayed on the carcasses of freshly slaughtered animals starting while they are still warm and continuing intermittently during much of the time required for chilling. This process not only achieves the purpose of controlling and reducing the number of bacteria but also minimizes shrinkage of the meat due to evaporation.
One of the unfortunate effects of the use of this process is the tendency of the chlorine solution to bleach the carcass skin. The use of a chlorine solution in a concentration strong enough to be reliably effective as a bactericide - say approximately 150 ppm - has been found to result in noticeable bleaching. In order to provide a concentration of chlorine sufficiently bactericidal, the concentration must be kept at or near the level which will result in at least slight bleaching; and it would first appear that the effectiveness of bactericidal treatment is signalled by the onset of bleaching. Further, at bactericidal levels, residual chlorine may present a slight odor, or alternatively may react with the bacteria to create an off odor which, although slight and not always present, is nevertheless undesirable.
Sprays of water alone, at sufficient pressure and volume, will of course partly cleanse meat of surface micro-organisms, but such washing of the meat results in its absorbing a great deal of water. This is not to be permitted (Journal of Food Science, Vol. 40 p. 1232).
Chlorine dioxide is well known as a bleaching substance and as an agent for treating water in air conditioning systems, as well as a bactericide. To the best information of the undersigned, it has not prior to the present invention been substituted for chlorine in misting or spraying hog carcasses during chilling. As discussed later herein, the chemical mechanisms by which it may kill germs or bleach cells are found to be different from those of chlorine.
In contrast to chlorine, which when added to water produces hypochlorous acid, chlorine dioxide must as a practical matter be generated at the point of application and mixed into the water. Chlorine dioxide is readily dissolved in water, but does not substantially hydrolize in water. There is only slight hydrolysis to chlorous and chloric acid.